Synthesis of gold nanoparticles in sol–gel glass porogens containing [bmim][BF4] ionic liquid

The [bmim][BF₄] ionic liquid effect on gold nanoparticles formation in silica sol–gel materials is studied in order to produce gel-derived glasses with optical properties. The characteristic red color from gold nanoparticles is observed for transparent glass monoliths obtained sintering, between 365 and 425 °C, a silica sol–gel precursor containing HAuCl₄·3H₂O and [bmim][BF₄], under normal atmospheric conditions. The effect of sintering the ionogel at different temperatures (T_sint) or times (t_sint) on the optical properties, shape, size, and distribution of gold nanoparticles is discussed. Presence of the gold particles is observed using transmission electron microscopy images followed by energy dispersive X-ray spectroscopy analysis. The thermal decomposition of [bmim][BF₄] in the ionogel is investigate using calorimetric and spectroscopic techniques, and by analysis of volatile compounds released by the sol–gel material during sintering. With these results a mechanism for the formation of the gold nanoparticles is proposed, where a first ionic liquid degradation step provides the reductive environment that enables the gold nanoparticles production at the range of temperatures between 350 and 425 °C. Upon sintering the synthesized materials the ionic liquid acts as a sacrificial additive and the ionic liquid thermal decomposition products enables the formation of gold nanoparticles in the sol–gel matrix.     

Synthesis of gold nanoparticles from gold(I)-alkanethiolate complexes with supramolecular structures through electron beam irradiation in TEM

Monodisperse gold nanoparticles were prepared via electron beam irradiation of Au(I)-SR (R = -CnH2n+1) polymers with highly ordered supramolecular structures in transmission electron microscopy. The Au(I)-SR polymers were synthesized simply by mixing LiAuCl4 and an excess amount of alkanethiol in tetrahydrofuran. The sizes of the gold nanoparticles were controlled by changing the length of the alkyl group or by adjusting the energy of the electron beam.     

Aggregation of photolytic gold nanoparticles at the surface of chitosan films

Formation and aggregation of photolytic gold nanoparticles at the surface of chitosan (CTO) films have been investigated. When thin films of chloroauric acid salt of CTO were irradiated with UV light in wet air at room temperature for 10 min, gold nanoparticles of approximately 10 nm size are formed at the film surface. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize gold nanoparticles at the film surface. The shift of Au(4f) peak to the higher energy side and broadening of full width at half-maximum in the XPS spectrum are the direct evidence of the existence of gold atoms and small clusters in the early stage of photolysis. According to FE-SEM observation, growth in the particle diameter and aggregation of nanoparticles were observed after prolonged irradiation, and, finally, the film surface was densely covered with gold particles of 20-100-nm size. Gold atoms and clusters could move in the film and precipitate to the irradiated surface. Chemical composition analysis further suggests that gold particles at the surface are covered with an ultrathin CTO layer, which is partly oxidized by oxygen and chlorinated by chlorine during photochemical reactions.     

Ultrasonic Synthesis of Gold Nanoparticles and Its Use in Immunochromatographic Assay for Detection of Kanamycin

An ultrasonic method to synthesize gold nanoparticles with uniform size was reported. Effects of ethanol concentration, solution pH, ultrasonic irradiation power, and time on the formation of gold nanoparticles were investigated. The obtained gold nanoparticles were characterized by ultraviolet-visible (UV-vis) absorption spectra and scanning electron microscope (SEM). The method performed in ethanol solution under ultrasonic irradiation is friendly to the environment. Furthermore, a nanogold-labeled probe was used to develop an immunochromatographic method for detection of kanamycin.     

Film formation of Ag nanoparticles at the organic-aqueous liquid interface

We report a wet-chemical method to make films by spontaneous assembly of passivated Ag nanoparticles at the organic-aqueous liquid interface. The interfacial films exhibit a blue opalescence and are characterized with transmission electron microscopy and UV-vis spectrophotometry. Measurements indicate that nanoparticles in the interfacial film can form superlattices and in some cases nanostructures.     

Photoinduced electron transfer between chlorophyll a and gold nanoparticles

Excited-state interactions between chlorophyll a (Chla) and gold nanoparticles have been studied. The emission intensity of Chla is quenched by gold nanoparticles. The dominant process for this quenching has been attributed to the process of photoinduced electron transfer from excited Chla to gold nanoparticles, although because of a small overlap between fluorescence of Chla and absorption of gold nanoparticles, the energy-transfer process cannot be ruled out. Photoinduced electron-transfer mechanism is supported by the electrochemical modulation of fluorescence of Chla. In absence of an applied bias, Chla cast on gold film, as a result of electron transfer, exhibits a very weak fluorescence. However, upon negatively charging the gold nanocore by external bias, an increase in fluorescence intensity is observed. The negatively charged gold nanoparticles create a barrier and suppress the electron-transfer process from excited Chla to gold nanoparticles, resulting in an increase in radiative process. Nanosecond laser flash experiments of Chla in the presence of gold nanoparticles and fullerene (C60) have demonstrated that Au nanoparticles, besides accepting electrons, can also mediate or shuttle electrons to another acceptor. Taking advantage of these properties of gold nanoparticles, a photoelectrochemical cell based on Chla and gold nanoparticles is constructed. A superior performance of this cell compared to that without the gold film is due to the beneficial role of gold nanoparticles in accepting and shuttling the photogenerated electrons in Chla to the collecting electrode, leading to an enhancement in charge separation efficiency.     

Electron beam irradiation of poly(vinyl methyl ether) films: 1. Synthesis and film topography

Temperature-sensitive hydrogel layers on silicon (Si) substrates were synthesized by electron beam irradiation of spin-coated poly(vinyl methyl ether) (PVME) films. The influences of the used solvent, the polymer concentration, and the spinning velocity on the homogeneity and the thickness of the PVME film were investigated. In the range of concentration c(p) = 1-15 wt% PVME in ethanol solution, homogeneous films with a thickness between d = 50 nm and 1.7 mum were obtained. The films were cross-linked by electron beam irradiation under inert atmosphere and analyzed by sol-gel-analysis. The results were compared with bulkgels formed by electron beam irradiation of PVME in the dry state. The film topography was analyzed by high-resolution field emission scanning electron microscopy and atomic force microscopy. An islandlike structure in the dry, swollen, and shrunken state of the hydrogel films was observed.     

Molecular simulation of interaction between passivated gold nanoparticles in supercritical CO2

Molecular dynamics simulations have been performed to study the potential of mean force (PMF) between passivated gold nanoparticles (NPs) in supercritical CO(2) (scCO(2)). The nanoparticle model consists of a 140 atom gold nanocore and a surface self-assembled monolayer, in which two kinds of fluorinated alkanethiols were considered. The molecular origin of the thermodynamics interaction and the solvation effect has been comprehensively studied. The simulation results demonstrate that increasing the solvent density and ligand length can enhance the repulsive feature of the free energy between the passivated Au nanoparticles in scCO(2), which is in good agreement with previous experimental results. The interaction forces between the two passivated NPs have been decomposed to reveal various contributions to the free energy. It was revealed that the interaction between capping ligands and the interaction between the capping ligands and scCO(2) solvent molecules cooperatively determine the total PMF. A thermodynamic entropy-energy analysis for each PMF contribution was used to explain the density dependence of PMF in scCO(2) fluid. Our simulation study is expected to provide a novel microscopic understanding of the effect of scCO(2) solvent on the interaction between passivated Au nanoparticles, which is helpful to the dispersion and preparation of functional metal nanoparticles in supercritical fluids.     

In situ formation and size control of gold nanoparticles into chitosan for nanocomposite surfaces with tailored wettability

The in situ formation of gold nanoparticles into the natural polymer chitosan is described upon pulsed laser irradiation. In particular, hydrogel-type films of chitosan get loaded with the gold precursor, chloroauric acid salt (HAuCl(4)), by immersion in its aqueous solution. After the irradiation of this system with increasing number of ultraviolet laser pulses, we observe the formation of gold nanoparticles with increasing density and decreasing size. Analytical studies using absorption measurements, atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy of the nanocomposite samples throughout the irradiation procedure reveal that under the specific irradiation conditions there are two competing mechanisms responsible for the nanoparticles production: the photoreduction of the precursor responsible for the rising growth of gold particles with increasing size and the subsequent photofragmentation of these particles into smaller ones. The described method allows the localized formation of gold nanoparticles into specific areas of the polymeric films, expanding its potential applications due to its patterning capability. The size and density control of the gold nanoparticles, obtained by the accurate increase of the laser irradiation time, is accompanied by the simultaneously controlled increase of the wettability of the obtained gold nanocomposite surfaces. The capability of tailoring the hydrophilicity of nanocomposite materials based on natural polymer and biocompatible gold nanoparticles provides new potentialities in microfluidics or lab on chip devices for blood analysis or drugs transport, as well as in scaffold development for preferential cells growth.     

Relaxation dynamics and transient behavior of small arenethiol passivated gold nanoparticles

Novel gold nanoparticles, passivated by monolayers of benzenethiol, biphenylthiol, and similar derivatives, have been synthesized and characterized using UV/vis, NMR, and Fourier transform infrared (FTIR) spectroscopies. The nanoparticle sizes have been evaluated using transmission electron microscopy and UV/vis spectroscopy; they show diameters between 2.1 and 4.7 nm, depending on the method of synthesis and the monolayer protecting group. Femtosecond transient absorption measurements show that the nanoparticles possess optical properties on the boundary between molecular and nanoparticle behavior. The smaller systems based on benzenethiol exhibit long-lived excited states with lifetimes on the order of a few nanoseconds, resembling those of small gold molecular type clusters. The larger nanoparticles protected with biphenylthiol and benzylthiol groups relax much more rapidly on a picosecond time scale, similarly to related citrate stabilized systems reported in the literature.     

Bimodal Size Distribution of Gold Nanoparticles under Picosecond Laser Pulses

The evolution of size distributions of gold nanoparticles under pulsed laser irradiation (Nd:YAG, lambda = 355 nm, pulse width 30 ps) was carefully observed by transmission electron microscopy. Interestingly, the initial monomodal size distribution of gold nanoparticles turned into a bimodal one, with two peaks in the number of particles, one at 6 nm and the other at 16-24 nm. The sizes for small particles depended very little on the irradiated laser energy. This change is attributed to laser-induced size reduction of the initial gold nanoparticles followed by the formation of small particles. In our analysis, we extracted a characteristic value for the size-reduction rate per one pulse and revealed that laser-induced size reduction of gold nanoparticles occurred even below the boiling point. When laser energy is insufficient for the boiling of particles, formation of gold vapor around liquid gold drops is thought to cause the phenomenon. With enough laser energy for the boiling, the formation of gold vapor around and inside liquid gold drops is responsible for the phenomenon. We also observed particles with gold strings after one pulse irradiation with a laser energy of 43 mJ cm(-2) pulse(-1), which is sufficient energy for the boiling. It is considered that such particles with gold strings are formed by the projection of gaseous gold from liquid gold drops with some volume of liquid gold around the bubble. On the basis of comparison with previous work, picosecond laser pulses are thought to be the most efficient way to cause laser-induced size reduction of gold nanoparticles.     

Tunable metallization by assembly of metal nanoparticles in polymer thin films by photo- or electron beam lithography

The technique of patterning of surfaces with metal-rich structures on micro- or nanoscales was developed by assembling metal nanoparticles into a thin film of polymer in a controllable way. Palladium (Pd) nanoparticles were incorporated into a thin film of poly(methyl methacrylate) (PMMA) using palladium (II) bis(acetylacetonato), Pd(acac)(2), as a precursor vaporized in a nitrogen atmosphere. Depending upon its dose, the irradiation of a PMMA film by UV light or an electron beam (EB) enhances its reducing capability against Pd(acac)(2). This dependency on dose can be used to control the formation and assembly of Pd nanoparticles. Using this technique, binary patterns consisting of metal-rich and metal-poor regions in the polymer film can be created simply by irradiating the surface of the polymer through a binary photomask. Besides the creation of binary patterns, it is also possible to create grayscale patterns where the density of Pd nanoparticles can be tuned to provide shades of gray by the use of light with continuously modulated intensity. Because the electron beam also enhances the reducing power of PMMA against Pd(acac)(2), it is thus possible to obtain highly metallized films with nanoscale pattern features. The PMMA film can be selectively removed by oxygen plasma treatment or by pyrolysis. Thus, highly metallized surfaces with binary or grayscale patterns can be obtained by selective removal of the PMMA films. The metallized regions possess relatively high resistivity against CF(4) plasma compared to the bare silicon surface; therefore, the metallized surface patterns can be transferred onto the underlying silicon substrate by CF(4) plasma treatment. Because of the nanosize effect of metal nanoparticles, the thermal treatment at 900 degrees C, which is significantly lower than the melting temperature of the bulk Pd, yields continuous metallic features by binding the assembled nanoparticles.     

Structural Instabilities in Passivated Gold Nanoclusters Induced by Electron Irradiation

In the new nanotechnology devices design, the stability of the systems is very important, in the present work we report evidences of internal and external changes of nanoparticles passivated by thiol molecules when they are irradiated under a high flux of an electron beam in the transmission electron microscope. High Resolution images were digitized and processed in order to identify the contrast changes produced by the atomic inside the nanoparticles. Fcc and decahedral nanoparticles cases are shown. Molecular dynamics calculations are also included in order to compare the experimental evidences with the cluster conditions of stabilities. Both theoretical and experimental results imply the occurrence of atomic and twining movements, and indicate that the n-alkyl thiol molecules prevent atomic movement and changes on the particle structure are not observed.     

Electrochemical synthesis of silver nanoparticles-coated gold nanoporous film electrode and its application to amperometric detection for trace Cr(VI)

A simple and rapid approach for the electrochemical synthesis of Ag nanoparticles-coated gold nanoporous film (AgGNF) on a gold substrate was reported. The solid gold electrode (SGE) was directly anodized under a high potential of 5 V, and then reduced to obtain gold nanoporous film (AuNF) by freshly prepared ascorbic acid. The Ag nanoparticles (AgNPs) were grown on the AuNF electrode by potential-step electrodeposition. The resulting AgGNF composites electrodes were characterized by scanning electron micro...     

Rapid micropatterning of mesoporous silica film by site-selective low-energy electron beam irradiation

Rapid microfabrication of mesoporous silica film at low temperature was achieved with low-energy electron beam (LEEB) irradiation. A mesostructured film (thickness approximately 200 nm), which was prepared through hydrolysis and condensation of tetramethoxysilane in the presence of hexadecyltrimethylammonium chloride, was irradiated with LEEB at 25 kV and 300 microA under pressures of 10 and 1000 Pa. The surfactant molecules can be eliminated completely at temperatures less than 40 degrees C after only 10 min (10 Pa) and 5 min (1000 Pa) of irradiation, resulting in conversion to a highly ordered mesoporous silica film without cracking. The LEEB-irradiated film also showed reasonable chemical resistance toward dilute hydrofluoric acid solution due to sufficient consolidation by cross-linking of silicate networks during the irradiation. The unirradiated regions were etched away preferentially to the irradiated areas; therefore, rapid micropatterning of the mesoporous silica film was possible by area-selective LEEB irradiation followed by chemical etching.     

新型双链表面活性剂DDOBA的合成与高单分散性憎水纳米金的制备

自行设计合成了新颖的苄胺型双链表面活性剂3,4-双十二烷氧基苄胺(DDOBA). 利用DDOBA/正丁醇/正庚烷/甲酸/HAuCl₄·4H₂O自发形成的水/油(W/O)型微乳液作为微反应器, 通过微波辐射下的甲酸还原法成功制备了DDOBA保护的憎水性金纳米粒子, 并通过紫外-可见(UV-Vis)光谱、透射电镜(TEM)、高分辨透射电镜(HR-TEM)和X射线衍射(XRD)等方法进行了表征和分析. 结果显示, DDOBA既可参与形成稳定的W/O型(油包水型)微乳液, 又可作为金纳米粒子的良好保护剂. 在合适的微乳液体系组成范围内, 用本实验方法可以获得高单分散性的憎水性金纳米粒子, 并能在空气/水界面上自动形成大面积短程有序的纳米金二维自组装膜.     

Gold nanoparticle enhanced charge transfer in thin film assemblies of porphyrin-fullerene dyads

Photoinduced vectorial electron transfer in a molecularly organized porphyrin-fullerene (PF) dyad film is enhanced by the interlayer charge transfer from the porphyrin moiety of the dyad to an octanethiol protected (dcore approximately 2 nm) gold nanoparticle (AuNP) film. By using the time-resolved Maxwell displacement charge (TRMDC) method, the charge separation distance was found to increase by 5 times in a multilayer film structure where the gold nanoparticles face the porphyrin moiety of the dyad, that is, AuNP|PF, compared to the case of the PF layer alone. Films were assembled by the Langmuir-Blodgett (LB) method using octadecylamine (ODA) as the matrix compound. Atomic force microscopy (AFM) images of the monolayers revealed that AuNPs are arranged into continuous, islandlike structures and PF dyads form clusters. The porphyrin reference layer was assembled with the AuNP layer to gain insight on the interaction mechanism between porphyrin and gold nanoparticles. Interlayer electron transfer was also observed between the AuNPs and porphyrin reference, but the efficiency is lower than that in the AuNP|PF film. Fluorescence emission of the reference porphyrin is slightly quenched, and fluorescence decay becomes faster in the presence of AuNPs. The proposed mechanism for the electron transfer in the AuNP|PF film is thus the primary electron transfer from the porphyrin to the fullerene followed by a secondary hole transfer from the porphyrin to the AuNPs, resulting in an increased charge separation distance and enhanced photovoltage.     

Photochemical synthesis of gold nanoparticles in N,N′-dimethylformamide via thiourea-derivatized polyoxometalate

In the present work, we report the photochemical synthesis of gold nanoparticles in N,N′-dimethylformamide by addition of a photocatalyst like thiourea-modified polyoxometalate (γ-SiW₁₂O₄₀). The polyoxometalate behaves as an electron relay. Reduction of the polyoxometalate takes place under UV irradiation followed by a transfer of electrons to the gold ions, leading to the formation of gold nanoparticles. The formation of the gold particles was monitored with time by UV–Vis spectrophotometry. The polyoxometalate also acts as a stabilizing agent and helps in controlling the size of the nanoparticles. The shape and size distribution was obtained from transmission electron microscopy studies. Spherical and monodisperse gold nanoparticles of ~10 nm size were obtained.     

Wetting properties of passivated metal nanocrystals at liquid-vapor interfaces: a computer simulation study

Molecular dynamics simulations have been employed to determine the contact angles of alkylthiol passivated gold nanocrystals adsorbed at the air-water interface. Simulations were performed using butane-, dodecane-, and octadecanethiol passivated nanoparticles. We demonstrate how the length of the surfactant chain can profoundly influence the wetting behavior of these nanoparticles. All particles were found to be stable at the air-water interface, possessing large, well-defined contact angles. We find that the shape of the dodecane- and octadecanethiol particles is strongly perturbed by the interface. We also present an analysis of the orientational ordering of water molecules at the dodecane-water interface and around butane- and dodecanethiol passivated nanoparticles. The orientational ordering translates into an electrostatic field around the nanoparticles, the magnitude of which corresponds with that of the water liquid-vapor interface.     

Solvation structure and dynamics for passivated Au nanoparticle in supercritical CO2: a molecular dynamic simulation

All-atomic molecular dynamics simulations have been performed to study the interfacial structural and dynamical properties of passivated gold nanoparticles in supercritical carbon dioxide (scCO(2)). Simulations were conducted for a 55-atom gold nanocore with thiolated perfluoropolyether as the packing ligands. The effect of solvent density and surface coverage on the structural and dynamical properties of the self-assembly monolayer (SAM) has been discussed. The simulation results demonstrate that the interface between nanoparticle and scCO(2) solvent shows a depletion region due to the preclusion of SAM. The presence of scCO(2) solvent around the passivated Au nanoparticle can lead to an enhanced extension of the surface SAM. Under full coverage, the structure and conformation of SAM are insensitive to the density change of scCO(2) fluid. This simulation results clarify the microscopic solvation mechanism of passivated nanoparticles in supercritical fluid medium and is expected to be helpful in understanding the scCO(2)-based nanoparticle dispersion behavior.